1) Field of the Invention
The present invention relates to polyester resins, and more specifically to siloxane-modified polyester resins excellent not only in non-tacky property, lubricating property, blocking resistance and the like but also in transfer resistance, bleed resistance and the like.
2) Description of the Related Art
Silicon compounds, especially siloxanes (silicone) oils have heretofore found wide-spread utility in application fields such as defoaming agents, release agents, textile treatment agents, various coating agents, paints, inks, and electrical or electronic parts or devices for their excellent properties such as non-tacky property, lubricating property, water repellency, flexibility and heat resistance. Siloxane compounds containing one or more reactive organic functional groups (active hydrogen atom) have also been used, whereby they have also been increasingly employed for the modification of resins and the like and for the treatment-of surfaces.
Siloxane-modified resins using such an activehydrogen-atom-containing siloxane compound are satisfactory in non-tacky property, lubricating property, blocking resistance and the like. The siloxane compound used as the modifier however contains one or more non-reactive siloxane compounds, which do not contain any active hydrogen atom, in a relatively high total proportion as impurities. Separation of such nonreactive siloxane compounds is very difficult because the non-reactive compounds and the reactive compound are not substantially different in physical properties.
Such non-reactive siloxane compounds are naturally contained as impurities in a conventional siloxane-modified resin. When a coating is formed with such a siloxane-modified resin, the non-reactive siloxane compounds contained as impurities undergo bleeding to the surface so that various problems are caused. A coating made of a siloxane-modified resin is crosslinked (hardened) with a crosslinking agent (hardening agent) upon its formation in many instances. The non-reactive siloxane compounds contained as impurities in the coating however do not react with the crosslinking agent, whereby the above-described problem of bleeding still occurs. The siloxane compounds thus bled then cause problems such that they may transfer to a material in contact with the coating and may smear the material or, when a magnetic layer of a magnetic recording medium or a back layer of a heat-sensitive recording material is formed with the above modified resin by way of example, they stick on a thermal head and considerably deteriorate the performance of the head.